Electron discharge device envelope having heat transfer element



D. E. ELECTRON DISCH HAVING HEAT July 30. 1968 2 Sheets-Sheet 1 FiledOct. 14, 1965 I I I 3 B W F w I m a w w I/ 75 5: w. m 5 wMm ::v w E m iA. |-.l I n .iMU n 3 Q 3 I M 8 Q N. a a- H 2 4 w 6 p 8 H 3 2 July 30.1968 o. E. MARSHALL ELECTRON DISCHARGE DEVICE ENVELOPE HAVING HEATTRANSFER ELEMENT 2 Sheets-Sheet 2 Filed Oct. 1.4, 1965 FIG.4.

E V R U C G W A l R l W l R W n R N U G C a m m A 8 A T RR 1 A O N E M HR n l. N m 0 0 0 00 000000 0 0 0 0 0 0 0 00 000000 0 0 0 0 O 0 O 40098765 4 3 2 l 5 4 3 2 I 20 3O 4O 6O 80 I00 I40 200 AVERAGE CURRENT PERIGNITRON -AMPERES United States Patent 3,395,300 ELECTRON DISCHARGEDEVICE ENVELOPE HAVING HEAT TRANSFER ELEMENT Donald E. Marshall, BeaverDams, N.Y., assignor to Westinghouse Electric Corporation, Pittsburgh,Pa., a corporation of Pennsylvania Filed Oct. 14, 1965, Ser. No. 496,0774 Claims. (Cl. 313-22) ABSTRACT OF THE DISCLOSURE This invention relatesto a pool-type rectifier in which a portion of the envelope surroundingthe discharge region between the anode and cathode includes a thicksection of material of high thermal conductivity and storage capacity.By this structure, heat generated within the envelope may be quicklyremoved from the inner surface of the envelope to provide increasedoperating capabilities of the pool-type rectifier.

This invention relates to electron discharge devices and moreparticularly to those in which a gaseous vapor is utilized.

A particular application of this invention is within a gaseous dischargedevice utilizing a pool-type cathode such as an ignitron. This inventionis particularly directed to ignitrons for applications wherein there isintermittent service demanded of the device.

During conducting periods, the ignitron provides relatively unlimitedelectron emission from the mercury pool cathode. The ignitron istherefore utilized in those applications where intermittent high currentdemands are found such as in welding systems. It is found that duringthese conduction periods that the heat generated within the ignitronresults in a substantial temperature rise in the envelope of theignitron. This in turn results in a rise in the mercury vapor pressurewithin the envelope. It is found within this high temperature enviromentthat frequent arc-back occurrences result. These arc-backs result inuneven heat control of the welds made and in some cases the unbalancedvoltages resulting therefrom cause transformer saturation to occur whichresult in complete operation failure. This adverse feature has beenaccepted by the industry and has been lived with mainly because mostapplications of the ignitron do not require the full rated capabilitiesof the tubes. However, often when attempts were made to use the fullcapability of the ignitron, trouble with too frequent arc-backsoccurred.

It is accordingly an object of this invention to provide an improvedelectron discharge device.

It is another object to provide an improved electron discharge deviceemploying a pool-type cathode.

It is still another object to provide an improved ignitron providing animproved cooling system for providing an increase in peak demand currentcapability and an increase in maximum average current capability.

It is still a further object to provide an improved igni tron in whichthe arc-back rate is greatly reduced.

Briefly, the present invention accomplishes the above cited objects byproviding a pool-type rectifier in which 'a portion of the envelopeincludes a thick section of high thermal conductivity material is goodthermal transfer relationship with the interior of the envelope. Acooling medium is associated with the thick section. The thick sectionprovided between the anode and the pool-type cathode is of high thermalconductivity material for providing heat storage capability and goodconductivity of the heat from the interior of the envelope to thecooling medium which may be circulating water.

Further objects and advantages of the invention will be- 3,395,300Patented July 30, 1968 come apparent as the following descriptionproceeds and features of novelty which characterize the invention willbe pointed out in particularity in the claims annexed to and forming apart of this specification.

For a better understanding of the invention, reference may be had to theaccompanying drawings in which:

FIGURE 1 illustrates a mercury pool tube of an ignitron type whichincorporates teachings of this invention;

FIG. 2 illustrates a modification of a portion of the envelope shown inFIG. 1 illustrating another embodiment of this invention;

FIG. 3 illustrates another modification of a portion of the envelopeshown in FIG. 1 and illustrating another embodiment of this invention;and

FIG. 4 are curves illustrating the properties of an ignitron accordingto this invention in comparsion with the properties of a prior artignitron.

Referring in detail to FIG. 1, there is shown a gaseous electricaldischarge device. The electrical discharge device comprises an innertubular member or casing 11 of a suitable material such as stainlesssteel. The cylindrical casing 11 is closed at the lower end by a platemember 13. The plate member 13 has a downwardly turned flange 15 aroundthe periphery of the plate 13. The plate 13 may be of a suitablematerial such as steel. The downwardly turned flange 15 of the member 13is seam welded to the lower portion of the casing 11. The end portion 14of the cylindrical casing 11 below the plate member 13 is flared outabout its periphery as illustrated. This flared end portion 14 is weldedto the inner surface of an outer tubular casing 17 at the lower end andthe outer casing 17. The outer casing 17 may also be of stainless steelof a thickness of about .060 inch.

The upper portion of the inner casing 11 also has a flared out portion12 and the external surface thereof is fitted against the inner surfaceof the upper portion of the outer casing 17 and is seam welded thereto.An annular space or region 19 is thereby defined between the two tubularcasings 11 and 17.

An opening 21 is provided in the outer casing 17 near the lower portionof the space 19 to permit the introduction of a cooling medium such aswater, or the like, into the space 19. Another opening 23 is providednear the upper portion of the space 19 in the outer casing 17 to providean outlet for the cooling medium introduced into the space 19. In thismanner, a cooling medium may be introduced into the space 19 and may becirculated throughout the space 19 from a source of cooling medium (notshown) for the purpose of reducing the temperature of the inner casing11. In the specific device shown, water guides 18 are also providedwithin the annular region 19 to increase the eifective cooling action ofthe circulating water. A heat conductive element 16 may also be providedbetween the inner casing 11 and the outer casing 17 of a suitable heatconductive material such as copper. The element 16 is in intimatethermal contact with the inner and outer casings 11 and 17. A thermostat20 may be provided on the outer surface of the casing 17 for sensing thetemperature of the interior surface of the inner casing 11. Thisthermostat 20 may be used for controlling the flow of cooling medium. Acircular lining 22 of a material such as copper is positioned within theinner casing 11 and is metallurgically bonded to the inner surface ofthe inner casing 11 by a suitable braze material. A suitable brazematerial is a stainless steel braze or a braze known under the tradenameNicro-Braze which is a nickel chrome alloy with boron, silicon orphosphor therein. This material may be obtained from the Colmonoy Corp.The liner 22 must be in good thermal contact with the inner casing 11and of a suitable high heat conductivity material such as copper. Othersuitable materials are aluminum, iron or brass. It is necessary toprovide a coating 24 over the copper member 22 of a material such asiron plate to protect the copper from attack by the mercury. Thiscoating 24 may be electroplated onto the copper to a thickness of about.002 inch to .010 inch. The thickness of the liner 22 is about .250inch, and extends down and makes contact with the plate 13. The upperportion of the member 22 is tapered as illustrated to be substantiallyparallel with the outer surface of an anode 46.

The plate member 13 which serves as a closure member for the bottomportion of the inner tubular member 11 also provided the bottom surfaceof a container for a mercury pool cathode 29. The pool cathode 29 isretained within the lower portion of the envelope formed by the plate 13and the adjacent wall of the liner member 22. A cathode terminal andsupport member 9 is welded or brazed to the under surface of the platemember 13.

An igniter electrode 31 is inserted into the mercury pool cathode 29 ina suitable manner. The igniter electrode 31 consists of a body of highresistance material such as boron carbide. The igniter 31 is supportedby an arm 33 which is in turn supported by rod 35 of insulating materialsuch as ceramic. The rod 35 passes through an aper ture provided in theplate 13. A terminal 38 is provided exterior of the envelope forapplication of potential to the igniter 31.

The anode 46 is of a suitable material, such as graphite, and ispositioned in the upper portion of the envelope. The anode 46 isprovided with a supporting conductive rod 48 which extends above theupper portion of the casings 11 and 17 to provide an external terminal40 for the anode 46. A plate or disc member 43 is provided having adownwardly turned flange 45 about its periphery. An aperture 26 isprovided in the center of the plate member 43 providing an openingthrough which the anode rod 40 passes. The disc 43 is welded to the rod40 about the aperture 26 to provide a vacuum tight seal. The platemember 43 is of any suitable material such as Kovar alloy (WestinghouseElectric Corporation trademark for an alloy of nickel, iron and cobalt).The annular edge of the downwardly turned flange 45 on the plate 43 issealed to the upper edge of a cylindrical member 28. The member 28 is ofa suitable insulating material, such as borosilicate glass. The loweredge of the glass cylinder 28 is sealed to the inner upwardly turnedflange 32 of an annular trough-shaped member 30. The outer surface of anouter upwardly turned flange 34 of the member 30 is welded or brazed tothe inner surface of the casing 11 below the flared out portion 12. Theinner flange 32 of the member 30 is of a similar material as platemember 43, while the remainder of the member 30 may be of steel. Theinner flange portion 32 is resistance welded to the remainder of themember 30. A shield member may be provided between the cathode 29 andthe anode 46 to further reduce possibility of arc-back in a well-knownmanner.

In FIG. 2, there is illustrated a modification of the invention shown inFIG. 1. The structure shown in FIG. 2 is modified in that a portion ofthe inner casing 11 is removed and the copper liner 22 is in directcontact with the cooling fluid. The liner or thick region 22 is providedwith a series of water guides 52 on the outer surface for improving thecooling of the member 22.

In FIG. 3, there is shown a liner 54 in which the inner surface isprovided with circumferential grooves 56 to increase the heat transferarea. This permits the use of a material such as iron. Iron is lessexpensive than copper and does not require a corrosion resistantcoating. Iron has a lower thermal conductivity than copper.

In the application of the ignitron, an alternating potential isimpressed between the anode 46 and the pool cathode 29. A discharge isinitiated between the cathode 29 and the anode 46 by means of theigniter assembly 31. By proper circuitry and associated controls, theperiods of conductivity of the ignitron can be controlled by the igniter31. In the specific application of resistance welding,

the ignitron is called upon to carry in some applications heavy currentfor the welding operation. This is normally an intermittent operationand therefore it is normal procedure that the tube be able to carry forbrief intervals current much in excess of that it could carry incontinuous operation. During the conducting period, the heat generatedin the tube must be removed or the increase in temperature will increasethe mercury vapor pressure. The likelihood of arc-back when the anode 46is negative with respect to the cathode 29 is greatly intensified. Thecooling system provided by the flow of the water between the inner wall11 and the outer wall 17 of the ignitron provides continuous cooling andof course would perform the function of cooling where the tube is incontinuous operation. However, in the case of the intermittent operationwherein the device is called upon to supply a current larger than thatnormally permitted in continuous operation, it is found that watercooling does not adequately provide the necessary protection of the tubefrom arcback. By providing the relatively thick section 22 of highthermal conductivity material a vastly improved ignitron is provided. Inaddition to the fact that the arc-back rate is greatly reduced over theprior art devices, it is also found that the ignitron provides a 60percent increase in peak demand current capabilities and a 60 percentincrease in the maximum average current capabilities for resistancewelding application. It is believed that this vast improvement isobtained by the heat storage capability of the thick wall portion 22.During the conductivity periods, the heat generated in the tube isabsorbed into the thick wall region 22. This reduces the amount oftemperature rise of the mercury condensing surfaces and thereforereduces rise of mercury vapor pressure in the tube. The lower vaporpressure results in much less tendency for arc-back thus improving thereliability of the tube. It is important that the thick wall section 22or 54 be made of a high heat conductivity material so that the heat thatis generated at the inner surface of the tube envelope can diffuserapidly from the inner surface into the depths of the thick wall 22 or54. It is important therefore that the corrosion resistive coating 24used with liner 22 also be of a high conductivity material or very thinin order to permit the dilfusion of the heat rapidly from the innersurface of the ignitron into the thick region 22. The water guides 18and 52 provided on the outer surface of the inner wall 14 provide a highvelocity water flow in this thick region and provide more efficientcooling. The thick wall 22 or 54 is used around the discharge region oftube in order to conserve the amount of the expensive high conductivitymaterial in comparison with stainless steel. It is also important thatthe low temperature cooling be provided near the mercury pool cathode29. It is found that less eflicient cooling in the region of the anode46 is advisable to provide for reduction of mercury condensation in theanode region which of course causes the arcback due to the mercuryparticles striking the anode. In addition, the bafiie 50 which isprovided between the pool cathode 29 and the anode 46 also provides afeature within the tube which reduces the frequency of arc-back. Thebaflle assembly 50 is to prevent mercury thrown by mechanical action ofthe arc on the cathode 29 from striking the anode 46. The tapered anode46 promotes the collection of electrons on the side of the anode 46 thusreducing current density at the anode face and thereby reducing theanode face temperature and the arc-back rate.

In FIG. 4, two curves are shown to illustrate the improved capabilitiesof this invention over the prior art type of ignitron. The verticalscale represents the demand current during the weld and the horizontalscale shows a corresponding maximum on time plus off time averagecurrent rating of the ignitron. Any points to the left of the curvesrepresents permissible operating condition for the tube. The areabetween the curves represents additional operating conditionspermissible 'for this invention described herein in contrast to theprior art.

The theory of water cooling teaches that white the water itself canabsorb large quantities of heat it does not make a perfect thermalcontact with the surface of the water jacket. In fact, the temperatureof the tube envelope under load is always greater than the watertemperature. This difference in temperature is directly proportional tothe energy density flowing from the water jacket surface to the water.If a tube is operated at about a 16 to 1 duty ratio, this temperaturedifference during conduction could be 16 times the value which would befound under continuous operations at the same long time average current.For comparable operation, the cooling surface would have to be 16 timesgreater in area for the on/off operation than for continuous operationat the average current. However, if the heat generated in the ignitronduring the on time can be stored in a mass of metal and then be cooledduring the off time, the 16 to 1 ratio of temperature rise can bematerially reduced. Previous ignitrons were designed withoutconsideration of the transient temperature rise of the envelope walls.To prevent corrosion caused by the Water cooling alloy steel were used.These materials are generally of low thermal conductivity. The diffusionof heat into the material is slow and the surface temperatures thereforeduring the on times rose to comparatively high values, resulting infrequent occurrence of arc-back.

Ignitrons according to the invention described herein exhibit arc-backfrequency many times lower than the prior art type of device. In fact,the improvement is so great that an increase in rating of these tubes ispossible to the degree shown in FIG. 4.

While there have been shown and described what are at present consideredto be the preferred embodiments of the invention, modifications theretowill occur readily to those skilled in the art. It is not desired,therefore, that the invention be limited to the specific arrangementsshown and described and it is intended to cover in the appended claimsall such modifications as fall within the true spirit and scope of theinvention.

I claim as my invention:

1. An electron discharge device comprising an envelope, said envelopehaving a pool-type cathode provided at one end thereof, an anodesupported above the cathode and defining the discharge regiontherebetween, said envelope comprising an outer cylindrical member ofstainles steel, an inner cylindrical member of stainless steel and aliner of a material having higher thermal capacity than stainless steelsurrounding said discharge region and being metallurgically bonded tothe inner surface of said inner member, said liner having a corrosionresistive coating thereon of less than .010 inch in thickness.

2. An electron discharge device comprising an envelope having apool-type cathode therein, an anode supported within said envelope andinsulated from said cathode and defining the discharge regiontherebetween, said envelope comprising a cylindrical portion and endplates for each end thereof, said cylindrical portion including an innercylindrical member and an outer cylindrical member, means providedbetween said inner and outer cylindrical member for conducting a coolingmedium to provide cooling of said inner member, a liner member thickerthan said inner cylindrical member bonded to the inner surface of saidinner cylindrical member, said liner of a material of higher thermalcapacity and thermal conductivity than said inner cylindrical member andpositioned so as to surround substantially said electron dischargeregion to provide heat storage and high conductivity of heat generatedwithin said envelope to said cooling medium.

3. An electron discharge device comprising an envelope, said envelopehaving a pool-type cathode provided at one end thereof, an anodesupported above the cathode and defining the discharge regiontherebetween, said envelope comprising an outer cylindrical member ofstainless steel, an inner cylindrical member of stainless steel and saidinner member including a portion of a material having higher thermalcapacity than said stainless steel surrounding said discharge region,said portion thicker than the remaining portion of said inner member toprovide heat storage and having a serrated inner surface to provide alarge area heat conducting surface.

4. An electron discharge device comprising an envelope having apool-type cathode therein, an anode supported within said envelope andinsulated from said cathode and defining the discharge regiontherebetween, said envelope comprising a cylindrical portion and endplates for each end thereof, said cylindrical portion including an innercylindrical member and an outer cylindrical member, means providedbetween said inner and outer cylindrical member of conducting a coolingmedium to provide cooling of said inner member, a liner member bonded tothe inner surface of said inner cylindrical wall member, said linermember of a material of high thermal capacity and thermal conductivityand positioned to surround at least said electron discharge region toprovide storage and high conductivity of heat generated within saidenvelope to said cooling means, said liner member being thicker thansaid inner cylindrical member having an irregular surface to provide alarge area to increase removal ratio of heat from said discharge region.

References Cited UNITED STATES PATENTS 2,121,579 6/1938 Bahls 313-20X2,224,750 12/1940 Slepian et al. 31318 X 2,433,181 12/1947 White 313-18X 3,045,138 7/1962 Pohl 313-21 DAVID J. GALVIN, Primary Examiner.

